Display screen or portion thereof with a graphical user interface



FIG. 1 is a front view of a display screen or portion thereof with a graphical user interface, showing a first embodiment of the new design;

FIG. 2 is a second embodiment thereof; and,

FIG. 3 is a third embodiment thereof.

The broken line showing an electronic device is for the purpose of illustrating environmental structure. All other broken lines illustrate the display screen and elements of the graphical user interface. Any subject matter that is shown in broken lines forms no part of the claimed design. 

CLAIM The ornamental design for a display screen or portion thereof with a graphical user interface, as shown and described. 